Existing networks typically operate in one of two modes, connection oriented mode or connectionless mode. In a connection oriented mode of operation, signals are communicated over specified paths from a source network element to a destination network element. Multi-Protocol Label Switching (MPLS) signals with, for example, Asynchoronous Transport Mode (ATM), Frame Relay, or packet-over-SONET encoding are examples of connection oriented signals. In a connectionless mode of operation, signals are communicated with less regard for the particular path traversed between source and destination network elements. Connectionless signaling typically focuses on the destination address, or other identification, rather than any particular path between source and destination network elements. Internet Protocol (IP), IPx, and SNA packet switching are examples of connectionless signal transport.
Connection oriented and connectionless communication each have their virtues. Due to the tracking of per-connection information in a connection oriented network, the connection oriented network provides efficient bandwidth management, which enables quality of service (Qos) aware services and traffic engineering ability. Connectionless networks, while generally less capable of providing quality of service aware services and traffic engineering capabilities, provide advantages over connection oriented networks in terms of their simplicity, reliability, and scaleability.
For example, connectionless networks do not generally require per-connection maintenance constructions to ensure complete state restoration upon recovery from a node failure. Rather, recovery from a nodal failure in a connectionless network typically only involves resynchronizing the routing database. In terms of scaleability, the connectionless network elements need only track the other network elements in the network, while the connection oriented network elements generally track each flow between various network elements. Because more than one flow can exist between network elements, the scaleability of connection oriented networks is generally limited if the network is to properly track various flow information. The lack of scaleability of conventional connection oriented networks has generally limited their applicability to geographically limited networks.
These and other network differences have generally resulted in connection oriented signals being transported over one set of network elements, while connectionless signals are communicated using another set of network elements. As a result, conventional network architectures, particularly wide area architectures have not supported both connectionless and connection oriented signaling.